Measurement of Microscopic Viscosity of Fluorescent Molecular Probe Doped in Biological Cell

孔雀石绿染料分子（MG）是一种三苯基甲烷染料，具有从光学激发态S_1到基态S_0的快速非辐射弛豫特性。在MG中，中心碳由三个苯环连接，激发态动力学受到局部环境微观粘度的强烈影响。黏度相关的非辐射过程被认为是由于MG的苯环围绕其轴的扩散旋转运动，这导致了从激发态到基态的内部转换。荧光衰减时间本质上是由局部环境的微观粘度决定的。荧光微探针在生物物体上的应用是非常有趣的，因为荧光测量非常敏感和无创。我们利用光学显微镜对洋葱细胞中MG的荧光衰减时间进行了测定，通过识别细胞间的相互关系甚至细胞内的位置。人们发现，衰减时间随细胞中的位置或细胞间的变化而变化。虽然荧光衰减时间差异的来源目前尚不清楚，但每个位点的显微黏度不同，可能反映了每个细胞生物活性的差异。近年来，光子计数可以测量非常微弱的荧光。如果该方法可以与光纤相结合，将来可能作为一种医学诊断方法。

Malachite green dye molecules (MG), a kind of triphenyl methane dye, are known for their very rapid nonradiative relaxation from the optically excited state S_1 to the ground state S_0. In MG the central carbon is joined by three phenyl rings and the excited state dynamics is strongly influenced by the microscopic viscosity of the local environment. The viscosity-dependent nonradiative process is thought to be due to diffusive rotational motion of the phenyl rings of MG around their axes, which causes the internal conversion from the excited states to the ground state. The fluorescence decay time is essentially determined by the microscopic viscosity of the local environment.The application of the fluorescent microprobe to biological objects is quite interesting, because the fluorescence measurement is very sensitive and noninvasive. We measured the fluorescence decay time of MG doped in onion cells by identifying one cell to another or even the position in a cell by using an optical microscope. It was found out that the decay time varies depending on the position in a cell, or one cell to another. Although the origin of the difference of the fluorescence decay time is not known at present, the microscopic viscosity of each site is different and it may reflect the difference of the biological activity of each cell. In recent years photon counting is possible to measure the very weak fluorescence. If this method can be combined with optical fibers, it may serve as a medical diagnostic method in the future.